NBSIR 75-748

Power Saws:

A Review of Injury Data and

Power Saw Industry Survey

V. J. Pezoldt

J. J. Persensky

Human Factors Sections

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1975

Final Report

Prepared for: Consumer Product Safety Commission

Washington, D. C. 20207

NBSIR 75-748

POWER SAWS:

A REVIEW OF INJURY DATA AND

POWER SAW INDUSTRY SURVEY

V. J. Pezoldt

J. J. Persensky

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1975

Final Report

Prepared for: Consumer Product Safety Commission

Washington, D. C. 20207

U.S. DEPARTMENT OF COMMERCE, Rogers O B. Morton/Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Oirectof

TABLE OF CONTENTS

Page

Acknowledgements iii

Summary v

1.0 imHODUCTION 1

2.0 HAZARD ANALYSIS 2

2.1 National Electronic Injury Surveillance System Data . . 2 2.2 In-Depth Investigation Reports Summary Data ...... 3

2 . 3 Summary 11

3.0 POIVER SAW SURVEYS 12

3.1 Summary of Survey Responses: Portable Cirailar Saws . . 13

3 . 2 Summary o£ Survey Responses : Table and Radial Arm Saws 18

4.0 DISCUSSION 22

4.1 Limitations of the Saw Surveys 22

4.2 Accident Data 23

4.3 Saw Design Issues 23

4.4 Are Saws Safe? 25

Appendix A - Glossary 27

Appendix B - Additional NEISS Accident Data 33

Appendix CI - Portable Circular Saw Survey Form 43

Appendix C2 - Tabulation of Responses to Portable Circular Saw

Survey 57

Appendix Dl - Table and Radial Arm Saw Survey Form 69

Appendix D2 - Tabulation of Responses to Table and Radial Arm

Saw Survey 85

Appendix E - Power Saw Manufacturers Surveyed 97

i

ACKNOWLEDGEMElsrrS

The authors of this report wish to acknowledge the assistance o£

Gail Hare in the development of the saw survey instruments and

Lester Milligan and Rudy Kelly for their aid in obtaining background

information and in the observational phase of the project. Thanks

are also due to Ann Ramey for her help in coding survey responses and

to Kim Howard for secretarial support.

iii

Summary

This document is the final report of an investigation of power saws performed for the Consumer Product Safety Commission (CPSC) . Two activities

of the project are described herein: a review of power saw injury data and

two surveys of power saw manufacturers ' individual opinions concerning

safety aspects of saw use and design. These surveys dealt with portable

circular saws and table and radial arm saws.

The injury data reviewed consisted of information from the National

Electronic Injury Surveillance System (NEISS) and from In-Depth Investigation

Reports ccmpiled by CPSC. The great majority of power saw related injuries

involved lacerations or amputations of the fingers or hands of males

over 15 years of age. The most detailed information about the patterns

of saw accidents was available for unspecified stationary saws and

portable circular saws. The most frequently reported accident patterns

involving stationary saws were "kickbacks," "hand in line with blade"

and "reaching over blade." For portable circular saws the two most often

reported accident patterns involved "kickbacks" and "guard malfunctions."

The two opinion surveys developed and administered by NBS were directed

toward obtaining the opinions of technical representatives of power saw

manufacturers on five major areas of saw use and design, i.e., electrical

safety, blade contact hazards and prevention, accidental starting of the

saw, the design of various saw components and the judged adequacy of saw instruction manuals. Power saw engineers and designers recognize some

probloTis with present saw designs, most notably these include the problems

associated with kickbacks. On the whole, however, those surveyed believe

saws to be reasonably free from hazards introduced by product design. The

area in which the saw manufacturers believe the most hazards to exist is

that of the operator's use of power saws. The human element in power

saw accidents is recognized as a major contributor to saw related injuries,

but little is known about how to assure that safe practices will be

followed. Areas for further study are suggested.

V

1.0 Introduction

This document is the final report o£ an investigation of power saws conducted by the National Bureau of Standards (XBS) for the Consumer Product

Safet}^ Commission (CPSC) . The major effort of the project was the development,

administration and analysis of two opinion sur\'eys directed toward the

manufacturers of (1) portable circular saws and (2) table and radial arm saws . Also included in the report is a summar>- hazard analysis based

on data provided by CPSC. >iich of the information presented in this

hazard analysis has been reported previously in a progress report.

Since its inception in January 1974, the power saw study has undergone several modifications in both direction and scope. As initially

conceived, this investigation was to encompass the identification of

power saw hazards and the evaluation of design characteristics , operator

safety practices , work space conditions and educational requirements for

safe power saw use. To this end, a four phase study was designed. The

first phase was an analysis of injury data to identif)^ the major hazards

and liazardous behaviors associated ^vdth documented power saw accidents. The

next three phases of study were to consist of progressively more structured

and controlled obser\^ations of power saws in use, beginning with unobtrusive

observ'ations under relatively natural conditions and culminating in controlled

laboratory observ^ations focusing on specific hazards of saw operation and,

possibly, design alternatives.

Coincident islth the initiation of the first phase of the formal

investigation, a variety of activities were pursued to acquaint project

personnel ivith saw use and design. These included informal consultation

wdth professional carpenters, woodworking instructors, saw retailers and,

perhaps most importantly, the development of a working relationship with the

Power Tool Institute (PTI) . The PTI is a major trade organization of power

tool manufacturers. Included in its membership are approximately 90 percent of

the portable saw manufacturers in the United States and a large proportion

of stationary saw manufacturers. Repeated contact with members of PTI's

Safet>' and Engineering Committees proved invaluable in facilitating the

learning process required by project staff. During this initial effort,

current voluntary standards were also reviewed.

The first phase of saw^ observations was initiated at several locations

including liigh school woodworking classes, apprentice carpenter training

sessions and a walk-in militar>' hobby shop. Approximately 10 hours of video

tape recordings were produced from these sessions. Content analysis of

the tapes , directed toward identif>'ing hazardous behaviors associated with

saw use, was initiated. Before completion, however, XBS was requested by

CPSC to change the direction of the investigation. These requests resulted

from a variety- of considerations including fiscal matters, modifications

in CPSC priorities and the ethical and legal ramifications related to the

Quarterly Report, Project 21, Power Saws , April 1, 1974.
use of human subjects. In another instance NBS was requested to stop all

ongoing activities in order to develop a response to a petition addressed to

the Commission concerning the owner's manuals which accompany power saws. This request was met by the transmittal of two memo reports to the CPSC

project monitor.

1

Negotiations relating to the status of the project led to narrowing

the project scope to one primary task, namely the development, administration,

and analysis of the two surveys of manufacturers' opinion. These surveys

were designed to elicit opinions on a variety of issues concerned with

safety aspects of the design and use of power saws. Topics addressed in

the surveys included electrical safety, blade contact, accidental

activation, design of saw components and the adequacy of instruction

manuals. The bulk of this report deals with the survey results.

To assist the reader who may be unfamiliar with the terminology

enployed in the saw industry and with the operations and components of

power saws, a brief glossary of important terms has been included in

Appendix A. Also included in this appendix are illustrations showing the

major components of portable circular, table and radial arm saws.

2.0 Hazard Analysis

A review of power saw accidents was made to provide information relevant

to the types of power saws reported to be involved in accidents , the kinds

of injuries sustained and the accident patterns involved. The data reviewed

were provided by CPSC and consisted of summaries of 282 In-Depth Investigation

Reports (IDIRs) and National Electronic Injury Surveillance System (NEISS)

data for FY 1973.

2.1 National Electronic Injury Surveillance System Data

Power saw accidents reported in NEISS are classified in four product

categories: power saws, not otherwise specified; power saws, portable, not

circular; power saws, stationary; and powered, portable circular saws. A

total of 1,483 incidents of personal injuries were reported in FY 1973 in

these categories. The majority of these, 1,114 cases (75 percent), involved

tools classified as unspecified power saws . Stationary and non-circular

portable saws each accounted for 140 (9.4 percent of the reported accidents

and portable circular saws 89 (6 percent) accidents. In light of the wide

variety of power saws available, these data provide little in terms of

identifying specific saw types which have been involved in accidents. There

is no way of ascertaining what types of saws were included in the unspecified

category. Furthermore, even the more specific categories likely include a broad range of saw types which are substantially different from each other in

both function and design. Thus, for example, radial arm, table and some jig

saws may all be classified as stationary saws even though they exhibit marked

differences in operation and design.

Power Saw Instruction Manuals, May 23, 1974, and June 24, 1974.

2
The NEISS data do provide information on the age and sex of accident

victims, body parts injured, injury diagnosis and location at which the

accident occurred. These data are presented in Tables 1-3 for all saw

classifications ccmbined. The data for each category separately are presented

in Appendix B. The overwhelming majority, 94.9 percent, of the victims was

male. Less than 10 percent of the victims were under 15 years old. In terms

of body part injured and injury diagnosis, lacerations of the fingers were by

fer the most common injury sustained, accounting for 60.3 percent of all

saw injuries. Hand and finger injuries account for 75 percent of all reported

saw injuries when the 59 incidents diagnosed as amputated fingers and the

159 cases of lacerated hands are added to these figures. Injuries which

involved lacerations or amputations of any body part constituted 88.9 percent

of all saw injuries. One diagnostic category in which there is a somewhat

surprising lack of reported cases is electric shock. Of 1,483 injuries

associated with power saws, only one incident of electric shock was reported.

IVhile this may be indicative of the electrical safety of power saws , there

is a possibility that electric shock injuries were under reported. Since

all of the accident data reviewed were reported by hospital emergency rooms

,

data on two important degrees of electric shock may have been lost.

Relatively mild shocks which resulted in immediate pain but required no medical attention could indicate potentially hazardous saws which the

accident data do not reveal. Similarly, any fatalities due to shock would

likely not be reported. Although NEISS injury data do not include industrial

or occupational injuries, a few injuries were reported as occupational.

These may have been injuries sustained by professional saw users at locations

other than an industrial installation, such as capenters working at private

residences. The only locations other than the home in which a substantial

number of accidents were reported occurred are listed in Table 3 as "other

public" locations. Slightly over 10 percent of the accidents were reported

as happening at these locations which include schools , public recreation

facilities and institutions.

2.2 In-Depth Investigation Reports Summary Data

The information from 282 IDIR summaries provide some additional insight

into power saw accidents . A summary of the data culled from the IDIR summaries

is presented in Tables 4-6. The value of these data lies not in the precise

numbers of incidents reported but rather in the charactization of the patterns

of saw accidents. It is important to note in this regard that the IDIR data

base is not a statistically representative base. Table 4 shows the distribution

of the accident victims' age and sex. Table 5 presents the body part injured

and injury diagnosis data. Overall these data are not markedly dissimilar

from the corresponding data reported in NEISS. Thus, the vast majority of

victims were male and the bulk of the injuries were lacerations and amputations

of fingers and hands. The NEISS and IDIR data do differ in terms of the

proportion of amputations reported. While only 4 percent of the incidents

reported to NEISS involved amputations, 19.5 percent of the IDIRs were so diagnosed. Another area in which the NEISS and IDIR data differ importantly is

in the distribution of saw types involved in reported injuries. Only 6 percent

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of the accidents reported to NEISS involved portable circular saws while

over 32 percent o£ the IDIR summaries deal with portable circular saws. Similarly, accidents involving non-circular portable saws comprise

9.4 percent o£ the NEISS data and only 3.2 percent of the IDIRs.

An effort was made to extract from the IDIR summaries information

concerning the types of sawing operations engaged in at the time of the

accident. Unfortunately, nearly half (46.4 percent) of the summaries

include reports of unspecified cutting or related activities. Of the

remaining incidents, the most commonly reported operation was ripping,

i.e., cutting with the grain of wood (24.1 percent) . It is unknown \\4iether

ripping appears more frequently than other operations because it is

inherently more hazardous or because it is one of the most commonly

performed sawing tasks. Nfost of the experienced saw users and manufacturers

consulted did agree that kickbacks were most likely to occur when ripping.

All other specified sawing operations (e.g., bevel, crosscutting) are

represented by less than 10 percent of the IDIR summaries.

The most important facets of the IDIR data are shown in Table 6. Data

in this table show the accident pattern of the reported incidents for each

saw type. The IDIR summaries provided somewhat more detailed information

on the types of saws in accidents than did the NEISS. Caution must still

be used in interpreting these data. For example, the category "unspecified

stationary saws" probably includes a wide variety of stationary saws. While most of these saws are table or bench saws , an unknown number may be

other types. The "accident patterns" specified in Table 6 offer a concise statement of the event or condition which precipitated the injury.

The accident patterns presented here were identified by CPSC. It should

be noted that these patterns may not be mutually exclusive.

2.2.1 Stationary Saws

For incidents involving stationary saws, the most prominent accident

patterns to merge fran the IDIRs were "kickbacks," "hand in line with

blade" and "reaching over the blade." Kickbacks can occur under several

conditions. Most commonly a kickback occurs when the kerf closes behind

the blade, thereby pinching the blade. The energy frcm the blade is then

transferred very quickly and usually unexpectedly from cutting through the

work to violently throwing it back toward the operator. A similar

result can be obtained if wood is fed into the blade from the wrong side.

As a result of consultation with PTI and other experienced saw users, it

has been learned that a variety of circumstances can increase the probability

that a kickback will occur. These include sawing badly warped or bowed

wood and improperly using a rip fence as a cut-off stop v^en crosscutting.

It is unknown what conditions prevailed in the majority of IDIR incidents

reported as kickbacks

.

Accidents in which the victims ' hands were in line with the blade

appear to have been the result of the operator inadvertantly pushing the hand

or fingers through the blade along with the workpiece. Reaching over the

10
blade occurred most often when the operator attempted to remove previously

cut pieces or scrap from the rear of the saw table without turning off the saw motor or waiting for the blade to stop rotating. It is not clear in

most of the accidents reported above whether or not a properly functioning

blade guard was in place at the time of the incident. The missing data are important since a properly used, well designed guard may have prevented blade

contact in many of these incidents. Without this information it is

impossible to attribute the occurrence of the accident to saw design or operator error.

2.2.2 Portable Circular Saws

Portable circular saws were involved in incidents having somewhat

different accident patterns than were stationary saws. Kickbacks were

again the most prominent pattern. While the causes of kickbacks may be

quite similar to those for stationary saws, the result is typically different.

Instead of the wood being kicked back at the operator, the saw itself is

often pushed violently out of the work. Guard malfunctions appear equally

as important a factor as kickbacks in portable saw accidents . The guard

involved here is the retractable lower guard. This guard, when functioning

properly, closes over the bottom of the blade when removed from the work.

The Underwriters Laboratory standard (UL45) to which most American saws conform specifies that retraction of the lower guard should be accomplished

within 0.3 seconds. It is not known whether the saws involved in accidents

described as guard malfunctions met this standard nor is the exact nature of

the malfunction specified for these incidents.

Two other accident patterns emerge quite often in portable circular saw

incidents. These are "reaching over the blade" and "inadvertantly starting

the saw." It is not clearly specified in the IDIR summaries what is meant

by "reaching over the blade." Given the design of common portable saws,

however, it is likely that these incidents might be more accurately

described as having a hand in line with the blade since the top

portion of the blade is covered at all times with a permanently fixed

guard. Inadvertantly starting the saw directly involves the design of the saw handle and grip and the location of the power switch, as well as the

operation required to activate the switch.

2 . 3 Summary

The review of power saw accident data provided some valuable insights

concerning power saw accidents. As might be expected, the great majority

of injuries involved lacerations or amputations of the fingers or hands of

males over 15 years of age. Seventy five percent of the injuries reported

to the NEISS involved power saws which were not specified as to type. The

IDIR summaries did provide some additional information relevant to specific

Standard for Portable Electric Tools, UL45. Fourth Edition, April 15, 1974,

Underwriters Laboratories, Inc.

11
saw types. These data, however, are not based on a known population of

accidents. The most detailed information was available for unspecified

stationary saws and portable circular saws. The former category includes

many types of stationary saws but most predominant among these are table

saws . Three accident patterns accounted for two thirds of the stationary

saw accidents reported in the IDIRs. These were "kickbacks," "hand in line

with blade," and "reaching over blade." Each of two accident patterns,

kickbacks and guard malfunctions, accounted for slightly more than 20 percent

of the injuries with portable circular saws. Nearly half (46.4 percent) of

the saw accidents reported through the IDIRs involved unspecified cutting

operations or related activity and more incidents occurred while ripping

(24.1 percent) than were reported for any other specified sawing operation.

3.0 Power Saw Surveys

The major effort of the power saw study performed by NBS has been

invested in the development, administration and analysis of two opinion

surveys directed toward technical representatives of manufacturers of

portable circular saws and table and radial arm saws. These surveys

were developed after a long process of familiarization with the products

currently on the market, review of CPSC accident data, observations of

power saws in use and meetings with representatives of the Power Tool

Institute.

The specific questions asked in the surveys were designed to elicit

opinions from saw designers and engineers about safety aspects of saw

design and use. Respondents were selected in cooperation with PTI and

consisted of members of PTI's Engineering Committee. Every member company

has at least one representative on this committee. Approximately 90 percent of

the portable circular saw manufacturers in the United States are members of PTI

and 85 to 95 percent of the table and radial arm saw consumer market is

accounted for by PTI member companies. A total of 19 surveys were sent to

portable saw manufacturers and four to makers of table and radial arm saws. Of the 19 portable saw surveys mailed out, 14 were returned completed, two

were returned uncompleted because the companies no longer manufacture

circular saws and three were returned not completed for other reasons. The

respondents to the portable saw survey are all professional engineers involved

in saw design "or research and development. The respondents to the survey

have an average of nearly 16 years in the saw industry and over 17 years

experience in the use of portable circular saws. Four surveys relating

to the table and radial arm saws were completed. The four respondents to

this survey average over eight years experience in the saw industry and

11 years experience in the use of table and radial arm saws.

The major topics addressed in the surveys were the same for both portable

circular saws and table and radial arm saws, i.e.:

1. Electrical safety 3. Accidental ignition

2. Blade contact hazards ^ 4. Design of saw components

prevention 5. Adequacy of instruction manuals

12
The specific questions in each of these areas were tailored to the

different saw types. The following sections summarize responses to the survey

items . A sample of the survey form and tabulation of answers to each of

the questions are presented in Appendices C and D. Because the respondents

sometimes gave multiple answers , or at times did not respond to a particular

item, the stated number of responses to a question may not equal the number

of respondents

.

3.1 Summary of Survey Responses: Portable Circular Saws

3.1.1 Electrical Safety

The portable circular saw survey addressed two topics relevant to

the electrical safety of saws: methods of assuring electrical integrity

and the use of ground fault interrupters.

3.1.1.1 Assurance of Electrical Integrity

Most manufacturers now make both double insulated and three -wire grounded

portable circular saws . Survey respondents were asked which type they

preferred for their own use and to express the advantages and disadvantages

of each. Eleven respondents preferred double insulated tools while only one preferred three-wire grounding. Two respondents had no preference. The most

commonly expressed advantage of double insulation was the ready availability

of appropriate receptacles, i.e., ungrounded two-pronged receptacles. Use of

double insulated tools, it was noted, requires no user initiated action to

assure electrical integrity. Two respondents also noted that cord and plug

sets on these tools can be replaced by amateurs without danger of

misconnection. The disadvantages of double insulation centered on the fact

that metal parts of the saw can become conductive if the saw cuts into an external power source such as a live wire or the power cord of the saw

itself. Other disadvantages mentioned included the opinions that double

insulated tools were scmewhat less durable and more prone to damage in

handling, were generally more expensive and might give the user a false

sense of security.

Opinions concerning grounded saws most often involved the problem of

not being assured of the integrity of the ground even when three -pronged

receptacles are available. For the most part, the advantages and disadvantages

of three-wire grounding were the converse of those for double insulation. Thus,

advantages expressed included the fact that grounding provides protection in

the event the power cord or other live wire is cut, more rugged construction

materials can be used for the saw housing and manufacture is less expensive.

3.1.1.2 Ground Fault Interrupters

The introduction of ground fault interrupters (GFI's) to home electrical

circuits is predicated on the premise that they provide an additional

margin of safety when electrical equipnent is used. The manufacturers were

asked to rate the extent of this added safety when using double insulated

13
and grounded saws. There was general agreement about the improved safety

of grounded saws which are integrated with a GFI , 13 respondents believed

the introduction of a GFI would moderately or greatly increase safety. Less

unanimity was evidenced concerning the impact of GFI's on double insulated

saws. Seven respondents replied that a GFI would provide a moderate or great increase in safety, while six others thought the GFI would add no safety

or maginal improvement at best.

3.1.2 Blade Contact Hazards and Prevention

Included in this section are summaries of the responses to questions

dealing with kickback prevention, braking systms, blade guards and

blade changing.

3.1.2.1 Kickback Prevention

Kickback was the most frequently reported accident pattern in the

CPSC IDIR summaries. Informal consultation with representatives of PTI

have indicated that the saw industry as a \^^ole has devoted much effort

to the kickback hazard. Therefore, a series of questions was asked

on this topic.

Many portable saws employ a so-called "slip clutch" as a means of reducing

kickback. When asked to rate the effectiveness of this device in reducing the

hazard, three respondents suggested that they were very effective, seven somewhat effective, one relatively ineffective and three of no use. When asked

to expand on the reasons for their ratings , there was general agreement

that while a slip clutch may reduce the probability of some kickbacks, thus

providing some margin of safety, there exists a major problan of adjustment.

That is, it is difficult to adjust the clutch such that the torque necessary

to cut wood is provided but, at the same time, this torque can be overcome

if the blade binds . It was also noted that the clutch does not necessarily

react quickly enough in the event of a very fast kickback.

Another approach to the kickback problem is the addition of a riving

knife or kerf guide to the saw. Many European saws incorporate this device but

most American saws do not. Therefore, we questioned the engineers on what they

felt were the advantages and disadvantages of riving knives. Ten respondents

suggested that a riving knife does reduce kickbacks (one of whom said it

eliminates kickbacks) and three also noted that it provides additional guarding

for the rear of the blade . All but two respondents , however , made mention

of serious adjustment problems when using a riving knife. These problems

stem from the fact that saw blades manufactured in the United States

are not standardized in terms of width or the set of the teeth. To be

functional, the riving knife must be slightly thicker than the face of the

blade but thinner than the kerf. Since blades vary considerably in width, the

matching of blades and knife becomes impractical . Problems also arise when

the riving knife is not exactly aligned with the blade. Two respondents

suggested that saw users would likely remove the riving knife. One manufacturer,

which does incorporate riving knives on its saws , indicated that approximately

90 percent of saws returned for factory service had the riving knife removed.

14
Another possible disadvantage o£ riving knives was suggested by two respondents

who claimed that the lower blade guard would be weakened by the slot

necessitated by the knife. The guard would be weakened to the extent that

the saw would no longer pass the drop test requironents of UL45. Finally,

three respondents noted the increased cost of adding riving knives to saws. A final issue related to kickbacks involved the extent to which dull

blades contribute to accidents in general and kickbacks especially. Three

respondents thought that for accidents as a whole dull blades were a major

cause, six said they contribute to a moderate amount of accidents and four

thought dull blades contribute only to a limited extent. By way of contrast,

dull blades were thought to contribute to kickbacks as follows: major

cause-six, moderate amount-five, limited extent-two. Asked to specify ways in

which a novice operator might be alerted that his blade is dull , most

respondents recommended including the warning signs in the instruction manual

.

One respondent, however, suggested the possibility of employing a low cost

force transducer that would excite a light emitting diode (LED) when the

blade became too dull for safe and efficient use

.

3.1.2.2 Braking Systems

A series of questions indirectly related to kickbacks but more directly

concerned with the general problem of blade contact was asked regarding

systems designed to quickly stop the blade. When asked to give opinions on

the merits of electronic brakes , which are activated when trigger pressure

is removed, all but one respondent mentioned some advantages. These

advantages were expressed in very general terms such as "provides fast stop,"

"reduces risk from coastdown injuries" and "provides back-up if guard fails."

Nine respondents also noted that electronic brakes greatly increase wear on

motor ccsnponents . Six of the engineers suggested that the technology currently

available for these brakes makes them unreliable. Other negative aspects

of electronic brakes included the expense involved, the violent action of

the brake which may startle the operator and the opinion that no braking

system currently available is fast enough to prevent kickbacks.

Asked to suggest alternative braking systems \\iiich might be considered

for protecting the user against kickbacks, seven respondents questioned the

value of any type of brake, and three recommended some kind of mechanical

system. The possibility of a system in which the blade is disconnected from

the motor and gear drive and a system which employs a brake operated by an

inertia switch was also suggested.

3.1.2.3 Blade Guards

Blades on portable circular saws are currently guarded by a stationary,

permanently attached top guard and a retractable lower guard which opens

as the blade enters the work and closes \A\en the blade is clear of the wood.

MDSt respondents considered the guarding requirements of IIL45 to be

adequate. Only one respondent replied favorably to the possibility of

extending the top guard beyond present requirements to prevent forward entry

15
of the operator's fingers. Negative responses centered around the reduction

in visibility introduced by such an extension and problems of clearance for

certain miter cuts . The saw engineers were equally negative concerning the

possibility of incorporating a stop of some kind to prevent raising the

lower guard above the shoe or saw table. Four respondents saw no advantage

to the addition of a stop and four suggested that it would only be

effective for very shallow cuts since, in the present design configuration,

the guard does not raise above the shoe when deeper cuts are made.

All but one respondent considered the present UL requirement for a ^ maximum time for the bottom guard to retract when removed from the work

to be valuable. Most agreed with the 0.3 second time allowed by UL45.

For a few operations, e.g., pocket cutting, it is necessary to retract

the blade guard manually before starting the cut. Respondents were asked,

therefore, to comment on the best location of the assist lever used to

raise the guard. Most respondents described configurations consistent with

UL45. The primary consideration was that the lever be in a position which

minimizes the possibility of contacting the face of the blade.

3.1.2.4 Blade Lock

Respondents were asked to rate the importance, in terms of safety, of

a blade locking system to facilitate blade changing. Nine members of the

sample thought such a device to be of minor or no importance while four thought

it moderately or very important. One respondent suggested that it might

be important for home saw users but not for professionals. The major reason

for giving low ratings for the value of a blade lock was that blade changing

can be accomplished safely without such a device as is evidenced by the lack

of reported accidents related to changing the blade.

3.1.3 Accidental Starting

Survey respondents were nearly evenly split on their opinions of the

feasibility of designing a starting system which would guard against accidental

triggering by children. Of those who accept the feasibility of this approach,

the majority of respondents favored a system employing a multistep ignition

process or a locking device when the saw is not in use. Some sentiment was

also expressed for incorporating stronger trigger pressure or longer switch

travel which would make it more difficult for children to start the saw.

3.1.4 Other Design Considerations

A series of questions relating to the design of various saw features

not previously discussed was included in the survey.

3.1.4.1 Shoe Design

Survey respondents were unanimous in the opinion that a full or wraparound shoe design is safer for the average home saw user than a halfshoe design. The advantages of a full shoe lie in the additional protection

16
it provides from blade contact and the added support and control of the

saw. However, half- shoes do have the advantage of allowing cuts closer to

walls and other obstructions . Opinion was split on the value of a removeable

shoe design. Seven respondents saw little or no advantage while five

reconiTiended the versatility of a "convertible" shoe v^ich allows the benefits

of both full and half shoe designs.

3.1.4.2 Auxiliary Handles

Responses were varied to the question related to operations for ^ich

an auxiliary handle or knob is appropriate. These ranged frcm all sawing

operations (three responses) and in particular ripping [four reponses)

,

to those instances in which the saw is used on other than flat surfaces or when extra control is needed (five responses) . ^fost respondents agreed that an auxiliary handle is at least somevdiat important as a safety device.

3.1.4.3 Cord Length and Location

IJL45 specifies a minimum cord length of six feet. Nine respondents

thought this an adequate length for safe saw use. Five others, however,

recommended lengths from 18 in to 15 ft (45.7 to 457.2 cm). A majority of

respondents agreed that an extensions cord is necessary for most operations

regardless of cord IsQgth.

The primary factors determining the location of cord entry into the saw were said to be to minimize the possibility of cutting the cord and to

provide for ease of saw operation.

3.1.4.4 Rip Fence

The rip fence or guide provided with most portable circular saws as either standard equipment or as an option was considered by most respondents

to be a convenience item. None considered it a safety feature.

3.1.4.5 Noise

Asked to rate the noise level of portable circular saws , eight respondents

thought the noise emitted was high (one said excessively high) and six

believe it to be acceptable. Several respondents noted that most of the

noise is generated by the saw blade cutting through the wood, not by the saw

motor. Only five respondoits considered a noise standard to be helpful for saw designers

.

3.1.5 Adequacy of Instruction Manuals

There ms general agreement that the instruction manuals which accompany

the saws need iinprovement both in terms of the written material and graphics

.

Itost respondents believed graphics should be used for the major sawing and

maintenance operations . The importance of effective instructions is well

recognized by the survey respondents, ^fost, in fact, suggested that a lack

of thorough reading of the manuals may be an important contributory factor in

power saw accidents

.

17
3.2 Sumiiiary o£ Survey Responses: Table and Radial Arm Saws

3.2.1 Electrical Safety

Table and radial arm saws are generally grounded and require the use of

three-pronged plugs . None of the survey respondents felt any benefit would

be realized by using double insulation for these saws. Present grounding

techniques were regarded to be adequate from a safety standpoint. The

introduction of a ground fault interrupter into circuits v\^ere grounded

stationary saws are used was viewed by two respondents as providing a moderate increase in safety. One respondent thought only a marginal

improvement would be realized and the fourth felt that the benefits of

GFI's were as yet unknown.

3.2.2 Blade Contact Hazards and Prevention

3.2.2.1 Kickback Prevention

Most table and many radial arm saws are equipped with splitters, or spreaders, and anti-kickback fingers. Splitters are designed to prevent

kickbacks by keeping the kerf open \\^iile the wood is being cut. Antikickback fingers are designed to negate the effect of a kickback, i.e., to

stop the wood from being thrown back at the operator. The effectiveness of

both of these devices in preventing injury from kickbacks was rated slightly

higher for table saws than for radial arm saws. Three respondents rated

anti-kickback fingers on table saws as moderately effective. On radial arm

saws this device was rated moderately effective by two respondents and

relatively ineffective by two others . Table saw splitters were rated very

effective in preventing kickbacks by two respondents and moderately effective

by one. For radial arm saws two respondents rated splitters moderately effective,

one relatively ineffective and one "does not prevent kickback." Only two

respondents noted any problems associated with the splitter when blades

of varying widths are used. One suggested that the splitter must be

slightly thinner than the kerf in order to function properly and the

other recoranended that splitter thickness should be sized to the thickest

blade used. It was also noted that the splitter must be properly aligned

with the blade. All respondents rated the task of accomplishing proper

alignment as relatively or very easy.

The contribution of dull blades was rated identically for both

kickbacks and accidents in general. One respondent thought they were a major cause, one rated dull blades as contributing a moderate amount to

accidents and two suggested that they contribute little or not at all to

kickbacks and other accidents . These opinions , though from a very small

sample, differ markedly from those expressed by portable circular saw

manufacturers , most of vAiom attributed more weight to the role of dull

blades in causing kickbacks

.

18
"h. 1.1.1 Braking Systems

The issue o£ incorporating a blade braking system on table and radial

arm saws is concerned primarily with possible hazards resulting from blade

coastdown. Two of three respondents did not consider coastdown to present

a hazard for the table saw user. The negative opinions were based on the

concept that the duration of coastdown on these saws is only a few seconds

and that the blade guard prevents any contact with the blade. The one engineer who believed that coastdown does present a hazard noted that the

saw user may reach for the cut wood or scrap before the blade stops . For

radial arm saws , which generally have a longer coastdown time than table

saws, two respondents believed coastdown is a hazard and two did not.

The reasons for these opinions were essentially the same as those noted

for' table saws. Two respondents felt the establishment of a maximum

time for coastdown to be completed would be advantageous , one reccmmended

15 seconds and the other thought the time should be dependent on blade

size.

Asked to specify the type of braking system they would prefer for

their own use, two respondents replied none for table saws and the third

suggested an "automatic brake." It is not exactly clear v^at is meant

by automatic in this instance beyond some system ^^^ich is not user initiated.

The four respondents replying to the same question in relation to radial

arm saws each gave a different response, i.e., manual, electronic, automatic

and none.

Survey respondents were asked to state the advantages and disadvantages

of manual and electronic brakes for table and radial arm saws. Overall,

the engineers were more receptive to incorporating a brake on radial arm

saws than on table saws. The major advantage attributed to electronic brakes was that they require no operator initiated action beyond turning off the

power switch. This advantage, however, was offset by the increased cost

introduced by electronic brakes and the opinion that they are subject to

malfunction. While manual brakes were consider cheaper and more reliable,

several respondents noted that they would likely not be used by many saw

owners. Almost no advantages were expressed for brakes of any kind on

table saws.

3.2.2.3 Blade Guards

Most table saws currently on the market are equipped with floating,

spreader mounted basket -type blade guards usually constructed of clear

plastic. Two respondents recommended this type of guard as being the best

for all crosscutting and ripping operations and suggested that it is the

best all around guard for home workshop use. This type of guard cannot be

used for non- saw- through (e.g., dadoing) or resawing operations. For these

procedures one respondent suggested a "barrier type guard" and the other

recommended a table mounted guard. A third respondent reccaranended a hinged

overhead guard, covering the top and sides of the blade, that tilts with the saw table and moves up and down with the wood for all operations. Custom

19
fitted tunnel guards were recanmended by one respondent for repetitive sawing

operations and the importance of dado and molding table inserts to support

the work and minimize the blade contact area for these special operations

was noted.

The retractable leaf guards, which cover the periphery of the blade, often

found on radial arm saws, were rated moderately effective by two respondents

and relatively ineffective by two others. One respondent suggested that

fully enclosed, see-through side guards are more appropriate and one recanmended tunnel guards for repetitive sawing operations.

3.2.2.4 Blade/Arbor Lock

Respondents were unanimous in the opinion that no advantage would be

gained from the inclusion of a blade or arbor lock to facilitate blade

changing. The present, conmonly employed procedure in which two wrenches are

used to change blades was generally supported. One respondent noted that

a blade or arbor lock could become accidentally engaged v^en the saw was

running, resulting in wear or failure of motor parts.

3,2.3 Accidental Starting

All respondents felt that present saw designs provide adequate protection

against accidental starting of the saw by children. The UL Standard for

Stationary and Fixed Electric Tools (UL 987) ^ requires that a tool shall be

provided with a means for locking the motor -control switch in the off

position. Such a locking systan was the method of choice for making saws "child-resistant" by all respondents except one who suggested there was

no need for this precaution.

3.2.4 Other Design Considerations

A series of questions related to other design features not previously

discussed were included in the survey.

3.2.4.1 Adjustment Interlock

Asked if it was technically feasible to design an interlock system

which vould prevent adjustments from being made vdiile the saw was running,

one respondent replied positively and two responded negatively. There was

unanijnity in the opinion that such an interlock would be undesirable in

that it would severely limit the use of the saw and provide an insignificant

advantage for much added expense and the potential for failure.

3.2.4.2 Sawdust Removal

No respondents evaluated a vacuum system for sawdust removal on table

saws as a safety feature, rather it was viewed as a convenience item. The

"Standard for Stationary and Fixed Electric Tools, UL987, Second Edition,

August 1, 1972, Underwriters Laboratories, Inc.

20
sawdust ejection feature on radial arm saws, on the other hand, ^s^as said to

be a safety feature by two respondents . Of interest is the fact that one respondent felt that such a feature is unnecessary and another had the opposite

view that it is a necessity.

3.2.4.3 Rip Fence

Unlike the rip fence used on portable saws, the rip fence employed with

table and radial am saws was rated as a necessary^ safety feature. All

respondents agreed that the rip fence was reasonably or ver>' easy to attach

and align properly and also convenient to use

.

3.2.4.4 Separate ^fo tors

In terms of overall operational safety, t\vo respondents regarded as reasonably safe the practice of marketing saws and motors separately.

One respondent considered this practice hazardous. Although no reason

was expressed for this opinion, it is assumed that the hazard referred

to involves the possible lack of skill and/or knowledge on the part of

the individual who installs his own motor

.

3.2.4.5 Radial Arm "Safety Return"

Some radial arm saws incorporate a system whereby the cutting head

automatically returns to a position behind the fence ^\iien the feed handle

is released. This is accomplished either by gravity or a spring system.

None of the sur\^ey respondents rated this feature as safe, tivo felt it is

slightly unsafe and two rated it hazardous. The primary reason cited for

these ratings was the loss of operator control of the cutting head. It was also noted that the so-called safety return may be fatigue inducing,

because the effort required to pull the saw through a crosscut is increased.

3.2.4.6 Radial Arm Grip (Feed Handle) Design

The most important consideration given by saw engineers in designing

the feed handle on radial arm saws is operator comfort. Safety and comfort,

of course, need not be mutually exclusive.

3.2.4.7 Accessories/Options

Very few optional features or accessories were recommended for the

novice operator of table or radial arm saws . I\vo respondents did

reccramend the addition of a miter gauge for table saws and a variety of

special purpose blades and cutters so that the consumer can take

advantage of the versatility of radial arm saws.

3.2.4.8 Noise

A consensus was not reached on the subjective evaluation of noise levels

for table or radial am saws. Ratings ranged from high to low. Similarly,

21
the respondents were evenly split on the question of the usefulness of

noise standards. Two believed they would be helpful and 2 thought they v^-ould

not

.

3.2.5 Adequacy of Instruction Manuals

In general, respondents to the table and radial arm saw survey rated the

instruction manuals which accompany the saws as satisfactory, although some need for inprovonent was recognized. These ratings were somev^t higher than

those for portable saw manuals. Generally the manuals for stationary tools

are more thorough than those for portable tools due in part to the greater

assembly requirements for stationary tools and the more complex operations

which may be performed with these tools.

4.0 Discussion

4.1 Limitations of the Saw Surveys

Before discussing the major issues raised in the power saw surveys,

several limitations of the surveys should be addressed. First, it must

be remanbered that all of the opinions expressed in the survey responses

are those of individuals whose jobs are directly tied to the design,

manufacture and distribution of saws now in the marketplace. This point

is not raised to cast any aspersions on the integrity of the respondents.

The degree of cooperation and openness v^tlich has been afforded by

that portion of the saw industry which was involved has been considerable.

Some degree of bias, however, is likely inescapeable and should be

recognized. It may be to CPSC's advantage, therefore, to obtain

additional opinions of other saw experts not directly associated with

the power saw industry, e.g., consumer groups, professional users and

instructors. This would, of course, require some modification of the

surveys to include issues which could be addressed by these individuals.

The number of respondents to the surveys was quite small . In the case of the portable circular saw (14 respondents) a substantial portion

of the industry was represented. There were four respondaits to the table

and radial aim saw survey. One of these answered, with a few exceptions,

only the questions dealing with radial arm saws. Thus, only three

individuals consistently responded to items related to table saws. While

this number is small , PTI estimated that the cc»i^nies represented hold

approximately 85 to 95 percent of the stationary saw market.

With the advantage of hindsight, it appears that table and radial arm saws might better have been addressed with two separate survey

instruments because of their unique designs and performance capabilities.

Also, throughout the course of the investigation more effort was devoted

to portable circular saws. The survey dealing with these tools was,

therefore, more complete and in some areas less ambiguous than the survey

concerned with stationary saws.

22
The majority o£ the items included in the surveys dealt directly with

the design o£ power saws. A thorough evaluation of power saw safety also

must consider the interaction between the saw and the saw user and should

not exclude the use environment. l\hile this interaction was implied in

several of the questions and alluded to in many of the reponses , the

surveys did not directly address user behavior. The behavior of saw

users was to have been the major focus of the observational phases of the

investigation w'hich, as noted previously, were terminated before completion.

4.2 Accident Data

Information about the role of the saw operator is often not included,

except in very general terms, in the accident data. The most specific data

about power saw accidents reviewed during the course of this project were

those involving portable circular saws and unspecified stationary saws. The most revealing facet of these data is that which relates to the

accident patterns involved in the incidents. IVhile this information does

give clues to possible hazards \vdth power saws , there are many important

considerations ishiich do not appear in the injury reports. Excluded from

most of the accident data are both specific information about the saw

and the behavior of the victim which resulted in the injury. The

physical characteristics of the wood or other material being cut, the

condition of the saw blade and the general condition of the saw itself

are important, but usually unknoim, elements in the occurrence of any

power saw related injury. On the human side, the seemingly elementary

question, 'HVhat did the victim do?" is often left unanswered. That the

vital role of the victim is usually not well specified is not necessarily

the fault of the data collection instrument or of the interviewer . In

many instances the victim himself may not be able to remanber or clearly

detail his actions immediately preceeding an accident. Nonetheless, the

lack of specific data does limit the researchers and the equipment designers

in their ability to draw conclusions ^vhich can be applied to the requirements

for safer products.

4.3 Saw Design Issues

For the most part, the responses to the saw surveys are self-explanatory

and require little in the way of further discussion. Several issues,

however, do deserve further consideration in light of their importance to

safe saw operation. The most significant problem associated with both

portable and stationary saws is kickback. This conclusion is dra\\TL from the

accident reports and the reported opinions of the power saw manufacturers

.

Saw designers have attempted to deal with this problon in a variety of

ways . These include the use of slip clutches , electronic brakes and

riving knives on portable saws and splitters and anti-kickback fingers on stationary saws . All of these approaches received some measure of support

from the respondents to the saw surveys but none were seen as the ccmplete

solution to the kickback problon. The riving knife merits special

attention in this regard, ^fost of the survey respondents were in agreement

that this device reduces the probability that a kickback will occur. The

opinions expressed regarding the positive aspects of riving knives, however.

23
were over ridden by two negative factors . The first was stated as a technical problem pertaining to the proper sizing and adjustment of the

knife when different saw blades are used. A second obstacle to the

incorporation of riving knives concerned the issue of consumer acceptance.

The opinion expressed by several respondents (as well as other saw manufacturers

not surveyed) that neither the American consumer nor the professional saw user will use a riving knife appears to be based upon some limited experience

in the United States and the experiences of European saw manufacturers

that currently do employ this device. Although this belief that consumers

will not accept riving knives as currently available may be valid, it is

also conceivable that if the technical problems with the knives can be overcome

consumers may be more willing to accept this device. Given the extent of

the kickback problem and the potential reduction in kickbacks which could

be realized, the issue of riving knives should be studied more thoroughly.

More generally, a research and development effort aimed at providing

unique means to prevent kickback would appear to be a highly worthwhile

pursuit

.

In addition to the problem of kickbacks , there are several other areas

in which saws may be deficient from a design standpoint. Most important

among these are guarding, accidental activation of the saw and the "safety

return" employed on seme radial saws. Hazards associated with these,

however, are not well defined in the accident data.

The question of guarding may not have been satisfactorily addressed

in the saw surveys. UL45 currently allows a maximum blade exposure of

25 degrees below the shoe (10 degrees if there is no outboard section of the

shoe when the retractable guard is fully extended. The guard must extend

at least to the root of the blade teeth. Above the shoe the blade may be

exposed a maximum vertical distance of 1 1/2 inches. European standards

require the moveable guard to totally enclose the face of the blade, with a maximum of 10 degrees blade exposure. Manufacturers have suggested that such

guarding would reduce visibility of the blade as it enters the material

being cut and would introduce clearance problems for some miter cuts. It

has been suggested that these limitations would be unacceptable to the consumer. In support of this notion, one European manufacturer stated

that the European guarding has been met with negative comments from

professional saw users in the United States. These comments are based

on the lack of visibility which infringes on the handling practices of

the professional user. Less is known, however, about the opinions of the

non-professional user. An investigation of consumer acceptance of

European type guarding in the United States or alternatively a study

of European experiences with consumer acceptance of these guards would

be beneficial to the clarification of the guarding question.

Accidental or unexpected operation of a cutting tool clearly can present

a serious hazard to the operator or to children playing with a saw. Stationary tools manufactured in compliance with UL 987 are required to

provide the capability for locking the power switch in the off position.

Although all survey respondents felt that this requirement provides adequate

24
protection against accidental starting of the saw, it should be noted that

the consumer may be required to provide his own lock. Voluntary

standards for portable saws do not include a locking requirement. While

the argument can legitimately be made that portable saws should not be left

unattended where children might have access to them, it is clear that this is

not always the case. Some portable saws do incorporate a means of protecting

against accidental starting through the use of a multi-step switch. These

switches require two distinct operations to activate the saw. In addition to

protecting children, these switches also protect the intended users vhen

they are carrying or moving the saw. A final issue related to a specific design feature of saws concerns

the incorporation of a so-called "safety return" on some radial arm saws. This feature returns the cutting head to a position behind the fence v^en

the feed handle is released after a crosscut is completed. Although this

feature may provide benefits in terms of convenience in production sawing

operations , the potential hazards resulting from lack of operator control

of the cutting head seem too great to justify including an automatic return

on saws for consumer use.

4.4 Are Saws Safe?

Based on the results of the opinion surveys and discussions with

saw manufacturers, several generalizations can be made concerning the saw

industry's opinions related to saw safety. On the whole, saw manufacturers

consider their products to provide adequately for the safety of the user. The manufacturers do recognize, however, that some potentially hazardous

situations, notably kickbacks, may be encountered vAien using a power saw. While reduction in the number of kickbacks may be achievable by

modifications in saw design, there is a general feeling among the

engineers that the interests of saw safety can best be served by improving

the skills and safety habits of saw users. The opinion was repeatedly

expressed that as more mechanical and/or electrical "safety features" are added to power saws the chances of failures which can result in additional

hazards are increased. If proper use of the saw is the best protection a difficult question still remains. How can proper use of power saws be

assured? The educational materials and safety and operating instructions

which accompany saws have not been sufficient to guarantee that saws will

be used in the safest manner.

In conclusion, it appears that the power saw industry is relatively

satisfied with the state-of-the-art with regard to the safety of their

products . However , they do indicate that there is seme need for

improvanent in two major areas. These are kickback prevention and user

instruction. In addition, this project has brought to light some questions

with regard to guarding, riving knives, unintentional starting and user

information. In order to adequately address these probl^is the following

research endeavors should be considered:

1. A research and developnent project to develop means to reduce

injuries associated with kickback.

25
A consumer acceptance test of both riving knives and more

extensive guards.

An evaluation of the potential hazards associated with accidental

starting of portable circular saws and the means to deal with them.

An investigation into improvement of user information techniques

which would involve not only content but also methods to induce

the user to read, remember, and use the information.

26
APPENDIX A

Glossary

The following definitions of terns used in the text are provided for

the reader unfamiliar with power saws and saw use:

Anti-kickback fingers - a mechanical device for gripping wood to prevent

it frcan being thrown toward the saw operator in the event of a kickback. Canmonly found on table and radial arm saws. See Figures

2 and 3.

Bevel cut - any cut made at other than a right angle to the horizontal

plane of the wood. See Figure 4.

Crosscut - a cut made across the grain of the wood. See Figure 4.

Dado - a non saw-through operation v^iich consists of cutting a rectangular

groove across the grain of a board. Dados can be acconplished by

making multiple cuts with a single saw blade or with the use of

special dado cutting heads.

Double insulation - a system of insulating power tools which uses a second

or "protecting" insulation system intended to protect the user fron

a shock in case of failure of the functional insulation. Construction

of double insulated tools varies from all metal exterior housings

to those having all exterior housings made of plastic.

Ground fault interrupter (GFI) - a device designed to detect electrical

ground faults and break the circuit when a fault occurs.

Kerf - the slit or notch made by a saw blade. Also, the width of the

cut made by a saw.

Kickback - the violent reaction of the wood or saw wiiich may occur vdien the saw blade binds in the wood. Several conditions may cause a kicldjack.

The most caimon of th^se occurs vvtien the kerf closes on the saw blade.

Leaf guard - a commonly used blade guard on radial arm saws. This type of

guard covers only the periphery of the blade and floats over the

material being cut. See Figure 3.

^^on saw-through operations - any of a variety of cutting operations in which a portion of a board is cut out but not sawed into two pieces, e.g. , dados,

rabbits

.

Resawing - ripping a board so the thickness is reduced or so that it is

made into two thinner pieces. See Figure 4.

27
Rip fence - on portable circular saws, an attachment which serves as a guide for making straight rips of a premeasured width. See Figure 1.

Used to guide the stock when making ripping cuts on a table saw. See figure 2.

Ripping - cutting with the grain of the board. See Figure 4.

Riving knife - an anti-kickback device on some portable circular saws. The

riving knife consists of a metal splitter blade (non-cutting) VN^iich

trails the saw blade to prevent the kerf from closing.

Shoe - the base of a portable saw. Three basic types of shoes are available

on these saws: full or wraparound shoe - extends completely around

the saw housing (See Figure 1) ; half -shoe - base is only on the inboard

side of the saw; removeable shoe - outboard portion of shoe can be

removed for making cuts close to an obstruction.

Slip clutch (kickproof clutch) - relieves motor strain and guards against

burnout, also designed to protect the operator fran possible kickbacks

if the blade binds.

Splitter (spreader) - an anti-kickback device consisting of a metal blade

mounted behind the saw blade to prevent the kerf from closing. See

Figure 2.

28
29
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32
APPENDIX B

Additional NEISS Accident Data

Distribution of Power Saw Accident Victims By Age and Sex

Table lA - Unspecified Power Saws

Table IB - .Nfon-Circular Portable Saws

Table IC - Stationar>' Saws

Table ID - Portable Circular Saws

Distribution of Injuries Related to Power Saw Use By

Body Part Injured and Diagnosis

Table 2A - Unspecified Saws

Table 2B - Non-Circular Portable Saws

Table 2C - Stationary Saws

Table 2D - Portable Circular Saws

33

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42
APPENDIX CI

Portable Circular Saw Survey Form

43

CMB 41-S-74105

Approval Expires June 30, 1975

NBS-1004

OPINION SURVEY

PORTABLE CIRCULAR SAWS

GENERAL INSTRUCTIONS : FOR EACH OF THE FOLLOWING QUESTIONS, PLEASE BRIEFLY STATE YOUR

OWN PERSONAL OPINIONS . WE ARE NOT INTERESTED IN YOUR COMPANY'

S

STAND- -ONLY YOUR OWN THOUGHTS ABOUT THE SAFETY ASPECTS OF POWER

SAWS. PLEASE KEEP THIS IN MIND WHEN ANSWERING QUESTIONS ABOUT

HYPOTHETICAL SITUATIONS CONCERNING THE "IDEAL" SAW. ALTHOUGH

WE REALIZE THE LIMITATIONS If-IPOSED BY THE CURRENT STATE-OFTHE-ART, WE ARE INTERESTED IN YOUR BEST JUDGEMENTS ABOUT THE

SAFE USE AND DESIGN OF POWER SAWS. PLEASE FEEL FREE TO MAKE

ADDITIONAL CCMMENTS IN THE MARGINS OR IN THE SPACE PROVIDED

AT THE END OF THE QUESTIONNAIRE.

1. Which type of connection would you prefer on a saw for you own use:

double insulated or three -wire grounding?

Double insulated

Three -wire grounding

la. In your opinion, what are the advantages of each type of connection

for portable circular saws?

a. Double insulated connections:

b. Three -wire grounding connections:
lb. How about the disadvantages of each?

a. Double insulated:

b. Three -wire grounding:

2. It is generally accepted that the introduction of ground fault interrupters to home electrical circuits provides an additional margin of safety

v^en electrical equipment is used. How would you rate the extent of this

added safety when using double insulated power saws?

Greatly increases safety

Nkxierate increase in safety

Marginal inprovement in safety

No added safety

2a. What about when using three -wire grounded power saws?

Greatly increases safety

Moderate increase in safety

Marginal inprovement in safety

No added safety

3. UL 45 specifies a six foot length of cord for circular saws. Do you

feel that this length is adequate?

Yes: Why is that?

No: What length would you consider adequate?

^feet

.

4. Cord location varies from saw to saw: some cords are located in the

base of the handle, some in the side of the grip, etc. What factors do

you think should determine the location of the cord on the saw? _____

46
5. Essentially, what factors do you think should determine the grip design

and location on circular saws?

a. Grip design:

b. Grip location:

5a. Do you have any preference for one design and/or location?

6. Do you think it is feasible for an ignition system to be designed which

guards against accidental triggering of the saw by children?

Yes : Have you any suggestions for its design? (General

comments, please):

No

6a. Which of the following do you feel should be considered as possible

methods by which an ignition system could be made "child resistant"?

Strong trigger pressure requirement for all saws Locking system when saw is not in use Multi-step ignition process, i.e., several operations

to be performed before saw starts

Other (specify)

None of the above ; no need for such precautions

47
7. How would you rate the effectiveness of a slip clutch in reducing

kickback hazard?

Very effective

Somewhat effective

Slightly ineffective

Of no use

7a. Why do you say that?

7b. Would you please list two or three major problems that you have

had with such a clutch?

8. In your opinion, what are the advantages of an electronic braking system:

8a. How about the disadvantages of an electronic braking system?

9, What other braking systems do you feel might be considered as alternatives

for protecting the user against kickbacks? (General comments, please):

48
10. Of what value do you think that the establishment of a standard time

for blade rotation to stop after disengagement of the power switch would be

Why?

11. How important is a blade locking system on saws in terms of a safety

device for blade changing?

Very inportant

Moderately inportant

Minor inportance

Not inportant

11a. Why do you say that?

12. Do you regard the sawdust ejection feature on some circular saws as:

Functional

A convenience item

A safety feature

Unnecessary

A necessity

12a. Are you aware of any problems with such a system?

Yes : What kinds of problems?

No

13. Where do you think that the assist lever should be located to raise

the bottom guard?

49
14. For what operations do you feel that an auxilliary handle or knob is

appropriate?

14a. If you were to rate the auxilliary handle or knob for its

effectiveness as a safety device, would you say that it is:

Very irportant

Somewhat inportant

Unnecessary

Not really a safety feature

15. Which shoe design do you consider safer for the average homeowner's

use: a full shoe or a half shoe?

Full shoe

Half shoe

15a. What would you say are the major advantages of each type of shoe?

a. Full shoe:

b. Half shoe:

15b. ttow about the disadvantages of each one?

a. Full shoe:

b. Half shoe:

SO
15c. Of what value, if any, is a removeable shoe?

16. Although European models have a riving knife incorporated into their

saws, iTKDSt American manufacturers do not. What do you think are the advantages of a riving knife?

16a. What about the disadvantages?

16b. What kinds of experiences have you had with a riving knife?

17. When you consider the use of a rip fence by a beginner, would you say

that it is primarily: (Mark only one of the below)

A safety feature

A convenience item

A "crutch" Viiiich he will learn to do without

A functiOTial necessity

Urjiecessary

17a. How would you rate the rip fence in terms of ease of attachment

and convenience to use. Very easy to attach Very convenient

Nfcxierately easy Moderately convenient

Somewhat of a bother Somewhat of a bother

Other (specify) Other (specify)

51
17b. What other features, such a guides and accessories, do you think

the novice operator should have?

18. Vlhat total percentage of the blade edge do you think it is feasible

to cover by guards?

19. What do you think would be the effect of attaching some sort of stop

that would prevent the bottom guard from being raised above the shoe?

19a. What about extending the top guard to prevent possible forward

entry of the operator's fingers?

20. In your opinion, would a standard maximum time for bottom guard

retraction be of value?

Yes: What time would you suggest? seconds

No

21. Ilow much do you feel that dull blades contribute to accidents in

general and kickbacks specifically?

Accidents Kickbacks

Major cause iMajor cause Moderate amount Moderate amount

Limited extent Limited extent

Little or none Little or none

52
21a. A dull blade is made obvious to the experienced saw user by

poor quality cut, burning of material, etc. Have you any ideas on ways to alert the casual user that his blade needs to be sharpened

or replaced?

Yes: Please explain:

No

22. How would you rate the noise levels emitted during the saw's operation?

Excessively high

High

Acceptable

Low

Other (specify)

22a. Are there any noise standards that you know of for circular

saw operations?

Yes : What are they?

No

22b. Do you feel that such a noise standard would be helpful?

Yes No

23. The following questions deal with the instruction or owner's manuals

provided with portable saws. Please answer these items based on your

familiarity with the manuals in general and your personal opinions of manual

effectiveness.

53
23a. Would you say that the graphics that are frequently used to

denvonstrate various saw operations are:

Satisfactory

Need inprovement

Other (specify)

2 3b . Do you prefer sketches or photographs of the various details

and operations that are presented in instruction manuals?

Sketches

Photographs

Other (specify)

23c. Would you say that the written instructions in the manuals are Satisfactory

Need improvement

Other (specify)

23d. For which of the following types of operations do you feel

graphic representation should appear in a manual? (Mark as many

as you think apply)

:

Rip cuts

Cross cuts

Pocket cuts

Identification of saw parts

Depth adjustment

Bevel adjustment

Use of rip fence

Cutting large pieces

Maintenance and care Other (specify)

54
23e. Could you suggest any way to further alert the user to the proper

and safe operation of circular saws?

23f . How much do you feel that the lack of thorough reading of the

instruction manual contributes to accidents?

23g. IVhat warnings do you feel should appear on the saw itself?

23h. The manuals of all meiT4>ers of the Power Tool Institute contain

a list of safety instructions developed by PTI. Are there any additional instructions or warnings you think should be included?

No

Yes, for exanple:

24. If you have any additional coirments or questions or areas not covered

in the survey please use the following space. If needed, attach additional

sheets

.

THANK YOU FOR YOUR TI>E AND EFFORT IN CCMPLETING THIS SURVEY. YOUR OPINIONS

AE MOST IMPORTANT TO US AND WILL BE TABULATED WITH THOSE OF THE OTHER

RESPONDENTTS. NO INDIVIDUAL IDENTITIES OF EITHER RESPONDENTS OR MANUFACTURERS

WILL APPEAR IN THE GENERAL SUNMARIES WE PLAN TO DEVELOP.

APPEMDIXC2

Tabulation of Responses to Portable Circular Saw Survey

Survey items in this appendix are presented in abbreviated

form. See Appendix CI for complete text.

57

Tabulation of Survey Responses: Portable Circular Saws

Preference:

11 - Double insulated.

1 - Three -wire grounding.

2 - No preference.

Advantages

:

a. Double insulation:

11 - Appropriate receptacles readily available, no user initiated

grounding action required.

2 - Cords and plugs replaceable by ajnateurs w/o danger of

misconnection.

1 - Uneffected in case of internal electrical failure.

1 - Infrequency of reported shock to user.

b. 3 -wire grounding:

7 - Provides protection in event cord or other live wire is cut

by blade.

5 - Safer, if integrity of ground assured.

3 - Allows use of more rugged construction materials,

1 - Protects against build-up of contaminants,

1 - Cheaper.

1 - No advantages.

Disadvantages:

a. Double insulation:

7 - Metal parts can become conductive if external power source

contacted.

2 - Less durable, more prone to damage in handling.

2 - May give user false sense of security.

2 - More expensive.

1 - Failure of both insulating systems possible.

1 - Possible for manufacturer to ship defects.

1 - No answer.

b. 3 -wire grounding:

12 - Properly grounded receptacles not always available, integrity of

ground may not be assured.

4 - Shock hazard if replacement cords and plugs incorrectly wired.

1 - Not protected if ground prong removed or improper extension

cord or adapter used.

Merits of ground fault interupter:

Double insulated saws Grounded saws

16

3

3

1

7

6

1

1

Greatly increases safety

Ntoderate increase in safety

Marginal improvonent in safety

No added safety

No answer

59
3. Is 6' cord length adequate:

9 - Yes - Miy? - 7 - Need extension cord for most operations.

1 - Adequate for bench operation.

1 - Any standard length will have shortcomings.

5 - No - IVhat length recommended

1 each - 18", 8', 10', 12', 15'.

8 - Minimize fxjssibility of cutting cord.

6 - Provide ease of operation.

3 - Minimize possibility of catching cord on work.

2 - No obstruction to users hands.

1 - Minimize interference with guard operation.

1 - Pulling on cord should not twist saw and bind blade.

1 - Electrical safety and economics.

1 - Provide operator with cord control.

1 - No answer.

5. Factors determining:

a. Grip design:

11 - Comfort.

2 - Prevention of accidental switch activation.

2 - Ease of switch operation.

2 - Positioned for best pushing angle,

3 - Hand size.

2 - "Safety".

1 - Insulated from metal portions of saw.

b. Grip location:

9 - Balance.

3 - Comfort.

3 - Back handle.

2-450 fpom plane of cutting surface.

1 - Visibility.

1 - As close to blade as possible.

5a Preference for grip design/ location:

10 - Respondents specified designs consistent vith above factors.

6. I'easible to design "child-resistant" ignition system:

6a Possible methods for making ignition system "child-resistant":

2 - Strong trigger pressure requirement for all saws.

6 - Locking system when saw is not in use.

6 - Multi-step ignition process, i.e., several operations to be

performed before saw starts.

3 - None of the above, no need for such precautions.

1 - Other: longer switch travel. '

4. Factors determining cord location:

8

- 6

- Yes.

No.

60
7. Effectiveness of slip clutch in reducing kickback hazard:

3 - Very effective.

8 - Somewhat effective.

2 - Slightly ineffective.

3 - Of no use. (one respondent marked each of first 3 alternatives)

7a Reasons for ratings:

Very effective:

Somewhat effective;

Slightly ineffective

Of no use;

2 - Provides margin of safety.

1 - Good, but can be defeated.

2 - Adjustment problems.

2 - Not effective in quick kickbacks.

1 - Reduces but does not eliminate kickbacks.

1 - Can be defeated.

1 - Users mist be educated to use clutch properly.

1 - No response.

1 - Adjustment problems.

1 - Can be defeated.

2 - Adjustment problems.

1 - None currently available that do job.

7b Major problems with slip clutch:

7 - Adjustment.

3 - No problems.

2 - No response.

1 - Reliable designs expensive.

1 - No real slip clutch exists.

8. Advantages of electronic braking systems:

6 - Fast blade stop.

3 - Reduces risk of coastdown injury.

2 - Back-up if guard fails.

2 - Reliable, tamper-proof.

2 - Safer.

1 - No advantages.

1 - No response.

8a Disadvantages of electronic brake:

9 - Wear on motor components.

6 - Unreliable.

3 - Expensive.

2 - Violent action, high arc may startle user.

1 - Defeats slip clutch.

1 - May encourage user carelessness.

1 - Not fast enough to prevent kickback.

61
9. Alternative braking systems:

8 - Question value of any braking system.

3 - Mechanical brake.

1 - System in which blade disconnected from motor ^ gear drive.

1 - Interim switch controlled brake.

1 - No answer.

10. Value of standard time for blade stop:

4 - Provides additional safety.

2 - Limited values.

2 - No value. ^ 2 - Not practical.

1 - Very valuable.

1 - Gives industry goal.

1 - Provides back-up if guard fails.

1 - No answer.

11. Importance of blade locking systan:

2 - Very important

.

3 - Moderately important.

6 - Minor importance.

4 - Not important.

(one respondent checked alternative 2 for home users, alternative 3 for

professional.)

11a Reasons for ratings:

Very important:

1 - Lack of such system encourages unsafe blade changing practices,

1 - Ensures proper bolt tension.

Ntoderately important:

1 - Operator that uses locking device probably would be safe

without lock.

1 - Professional doesn't need it, more adept than homeowner.

1 - Personal judgment.

Minor importance:

2 - Saw is not running when blade is changed.

1 - Could add hazard.

1 - Adds unnecessary cost.

1 - Not necessary if user follows safety precaution.

1 - Professional doesn't need it, more adept than homeowner.

1 - Few blade changing accidents.

Not important:

2 - Not necessary if safety precautions followed.

2 - Few or no blade changing accidents.

62
12. Sawdust ejection feature:

10 - f-'unctional

.

3 - Convenience item.

5 - Safety feature.

0 - Unnecessary.

3 - A necessity.

12a Any problems with sawdust ejection system:

9 - No.

1 - No response.

4 - Yes.

Kinds of problems:

3 - Clogging under some conditions, e.g., damp wood.

2 - Misdirection of discharge into users face.

13. Preferred location of bottom guard assist lever:

5 - Long enough to keep fingers away from blade.

2 - Inboard side of top blade guard.

2 - Extended radially beyond outer diameter of upper guard, bent

away from open face of blade.

2 - Top rear.

1 - Such that upper guard separates grasping point of lever and

blade.

1 - Per UL45.

1 - No response.

14. For v^t operations is auxilliary handle appropriate:

4 - Ripping operations.

3 - All sawing operations.

2 - When saw is used on other than flat work,

2 - Where extra control is required, e.g., crosscutting narrow pieces.

2 - When using heavy saws.

1 - When accuracy of start is important.

2 - No response.

14a Effectiveness of auxilliary handle as a safety device:

4 - Very important.

5 - Somewhat important.

0 - Unnecessary.

2 - Not really a safety feature.

4 - No response.

(one respondent checked very important for high capacity saws and

somewhat important for other saws.)

15. Safer shoe design for home use:

12 - Full shoe.

0 - Half shoe.

2 - No response.

65
15a Advantages of shoe types:

a. Full shoe:

10 - Provides additional protection from blade contact,

9 - Pro\/ides additional support, control, stability,

2 - Permits use of miter guide,

1 - Improves cutting accuracy.

3 - No response.

b. Half shoe:

10 - Permits cuts closer to obstructions,

1 - Permits better visibility.

1 - Lighter weight.

1 - Less expensive.

3 - No response.

15b Disadvantages of shoe types:

a. Full shoe:

7 - Cannot cut close to obstructions.

1 - Slightly poorer visibility.

1 - More expensive.

' 1 - Heavier.

1 - Damage to shoe could effect guard operation.

3 - No response.

b. Half shoe:

10 - Provides less protection.

6 - Provides less stability, support.

1 - Decreased accuracy of cut.

15c Value of removeable shoe:

7 - Very little or no value.

5 - Additional versatility, allows advantages of both full and

half shoe designs.

; 3 - No response.

16. Advantages of riving knife:

9 - Reduces kickback.

3 - Provides additional guarding of rear of blade.

2 - No advantages.

1 - Eliminates kickback.

2 - No response.

16a Disadvantages of riving knife:

11 - Adjustment problems due to variable saw blade thickness etc.

3 - Added cost.

2 - Users likely to remove.

2 - Weakens lower guard.

1 - Difficult to make pocket cuts.

1 - Less visibility.

1 - Learning problem for novices.

2 - No response.

64
16b Experience with riving knife:

4 - Limited or no personal experience.

?> - Used for evaluation purposes.

3 - Positive, promotes confidence in kickback prevention.

1 - 901 of returned saws minus riving knife.

1 - Binding in rip cuts.

2 - No response.

17. To novice saw user, rip fence is primarily:

0 - Safety feature.

11 - Convenience item.

2 - Crutch which user will learn to do without.

1 - Functional necessity.

0 - Unnecessary.

17a Rip fence ratings:

Ease of attachment

4 - Very easy.

8 - Moderately easy.

1 - Somewhat of a bother,

1 - No answer.

Convenience of use

4 - Very convenient

.

6 - Moderately convenient,

2 - Somewhat of a bother.

2 - No answer.

17b Other features, accessories novice should have:

3 - None.

4 - Gbod instructions.

2 - Miter guide.

2 - Good extension cord.

2 - Proper wrench for blade changing.

1 - Various blades.

1 - Vacuum pickup.

1 - Safety glasses.

1 - Plastic window to view blade position.

2 - No response.

18. Total percentage of blade feasible to cover by guards:

6 - 80-85%.

3 - 90-951.

2 - 75-80%.

2 - Per UL45.

1 - No response.

19. Effect of incorporating a stop to prevent raising bottom guard above shoe:

4 - No advantage.

4 - Only effective for very shallow cuts, otherwise guards already

function in this way.

2 - Likely to be removed by user.

1 - Contribute to saw safety if made adjustable.

3 - No response.

65
19a Effect of extending tcjp guard:

5 - Introduces visibility problems.

3 - Present guarding standards adequate.

2 - Introduces clearance problans for miter cuts.

1 - Technical disadvantages.

1 - Receptive to idea.

2 - No response.

20. Is standard maximum time for bottcwn guard retraction valuable;

1 - No.

1 - No response.

12 - Yes.

Time recormiended

8 - .3 sec.

2 - . 5 sec

.

2 - No response.

21. Contribution of dull blades to accidents:

In general Kickbacks

Major cause 3 6

Moderate amount 6 5

Limited extent 4 2 Little or none 0 0

No response 1 1

21a Ideas about how to alert casual saw user that blade is dull:

10 - Through instructions.

1 - Use of low cost force transducer that would excite LED.

2 - Have no ideas.

1 - No response.

22. Noise level ratings:

1 - Excessively high.

7 - High.

6 - Acceptable.

0 - Low.

1 - No response.

22a Are you aware of any noise standards for circular saws:

6 - No.

1 - No response.

7 - Yes.

What Standards

4 - OHSHA.

3 - PTI test method.

2 - Local or company.

66
22b Would noise standards be helpful:

7 - No.

5 - Yes.

2 - No response.

23. Adequacy of instruction manuals:

23a Adequacy of graphics:

5 - Satisfactory.

8 - Need improvanent

.

1 - No response.

23b Preference in graphics:

7 - Sketches.

4 - Photographs.

1 - Both.

1 - No preference.

1 - No response.

23c Adequacy of written instructions:

2 - Satisfactory.

11 - Need improvement.

1 - No response.

23d Graphic representation should appear in manuals for:

10 - Rip cuts.

10 - Crosscuts.

11 - Pocket cuts.

12 - Identification of saw parts.

11 - Depth adjustment.

11 - Bevel adjustment.

11 - Use of rip fence.

7 - CXitting large pieces.

10 - Maintenance and care. Other (specify)

2 - Use of miter guide.

2 - Types of blades.

2 - Changing blades.

1 - Sharpening blades.

1 - Recognition of dull blades.

1 - Use of riving knife.

1 - No response.

67
23e Way to further alert user to proper and safe saw operation:

4 - Provide warnings about unsafe practices.

3 - Make instruction manuals unique, alert saw owner to use them.

3 - Provide audio visual aides, posters etc.

2 - Provide more information about proper techniques.

23f How much does lack of thorough reading of manuals contribute to accidents

12 - Contributing factor.

2 - Not contributing factor.

23g IVhat warnings should appear on the saw itself:

6 - Consult operators manual.

3 - Check blade guard.

2 - Disconnect plug when chianging blade.

2 - Grounding instructions.

2 - Tool dangerous if used improperly.

1 - Keep blade sharp

.

1 - As required by UL45.

1 - As many as possible.

1 - Cannot put all warnings on saw.

23h RecOTtnendations for additional warnings in manual beyorid those PTI

members now include:

11 - No.

3 - Yes.

2 - Warning re grounding operator.

1 - Warnings re improper connections when changing cord set.

68
APPENTIX Bl

Table and Radial Arm Survey Form

69

NBS-1005

CMB 41-S-:'4105

Approval Expires June 30, 1975

OPINION SUR\TY

TABLE AND RADIAI. APM SAWS

GENERAL INSTRUCTIONS : FOR EAQI OF THE FOLLOWING QUESTIONS, PLEASE BRIEFLY STATE

YOUR OV^ PERSC^ OPINIONS . WE ARE NOT INTERESTED IN YOUR

COIPANT'S STAND- -ONLY YOUR OWN THOUGHTS ABOUT Tl-E SAFETY

ASPECTS OF POWER S^WS. PLEASE KEEP THIS IN MIND WHEN

^\SWERING QUESTIONS ABOUT HYPOTHETICAL SITUATIONS CONCERNING

THE "IDEAL" SAW. ALTHOUGH WE REALIZE THE LIMITATIONS IMPOSED

BY THE aT^RENT STATE-OF-THE-ART, WE ARE INTERESTED IN YOUR

BEST JUDGH^IENTS ABOUT ITE SAFE USE AND DESIGN OF POWER SAWS.

PLEASE FEEL FREE TO MAKE ADDITIONAL CO^iENTS IN THE MARGINS

OR IN THE SPACE PROV^IDED AT THE END OF THE QUESTIONNAIRE.

1. Kickbacks are involved in many of the injuries associated vdth table

saws. How would you rate the effectiveness of anti-kickback fingers in

preventing injury from a kickback on a table saw?

Very effective

Moderately effective

Relatively ineffective

Provides no protection

Introduces additional hazard (specify)

la. How would you rate the anti -kickback fingers commonly found on

radial arm saws ?Very effective

Moderately effective

Relatively ineffective

Provides no protection

Introduces additional hazard (specify)

71
2. Would you briefly describe the functions of a splitter (or spreader)

on table and radial arm saws?

a. Table Saw:

b. Radial Arm Saw:

2a. How would you rate the effectiveness of a splitter/spreader in

preventing kickbacks on table and radial arm saws?

Table Saws Radial Arm Saw

Very effective Very effective

Moderately effective Moderately effective

Relatively ineffective Relatively ineffective

Does not prevent kickbacks Does not prevent kickbacks

3. Can you think of any other ways to protect the user from kickbacks,

especially when the splitter/spreader would not be attached as is sometimes

the case for table saws?

4. Do you know of any problems that have arisen with the splitter/spreader

when blades of varying widths hiave been used? (Please ejqjlain briefly)

:

4a. Any other problems?

72

J
5. The splitter/spreader has to be renxDved for some operations and then

re-attached to the table saw. How difficult do you think it is for the

novice user to properly align the splitter/ spreader with the blade after

such operations?

Extremely difficult for the novice

Moderately difficult

Relatively easy

Very easy

6. If you were going to purchase a splitter/spreader for your own use,

what kind of material would you prefer it to be made of? Why is that?

7. A blade guard is standard equipment on almost all table saws. Different

types of guards, however, may be more or less appropriate for specific sawing

operations. In terms of the safest operating conditions possible, please

describe what, in your opinion, would be the best type of guard for each of

the following operations:

Operation Type of Guard

Cross -cutting short or medium length

stock

Cross -cutting long stock

Ripping narrow boards

Ripping large plywood sheets

Non saw- thru operations, e.g., dadoing

Resawing

7a. Are there any other types of guards that you feel are appropriate

for special operations?

Yes: Please describe the operation and type of guard:

No

73
5. The splitter/spreader has to be reiroved for some operations and then

re-attached to the table saw. How difficult do you think it is for the

novice user to properly align the splitter/spreader with the blade after

such operations?

Extremely difficult for the novice

Moderately difficult

Relatively easy

Very easy

6. If you were going to purchase a splitter/spreader for your own use,

vdiat kind of material would you prefer it to be made of? Why is that?

7. A blade guard is standard equipment on almost all table saws. Different

types of guards, however, may be more or less appropriate for specific sawing

operations. In terms of the safest operating conditions possible, please

describe what, in your opinion, would be the best type of guard for each of

the following operations:

Operation Type of Guard

Cross -cutting short or medium length

stock

Cross -cutting long stock

Ripping narrow boards

Ripping large plywood sheets

Non saw- thru operations, e.g., dadoing

Resawing

7a. Are there any other types of guards that you feel are appropriate

for special operations?

Yes: Please describe the operation and type of guard:

No

73
9a. Do you think that this blade rotation presents any hazard to the

radial arm saw user?

Yes : Why?

No: Why not?

9b. In your opinion, would there be any advantages to establishing a maximum allowable braking time for such situations?

Yes: What would you suggest? seconds

No: Why not?

10. What type of braking system would you prefer to have on a saw for your

own use?

For Table Saws For Radial Arm Saws

Manual Manual

Electronic Electronic

Other Other

None None

10a. Please list what you feel are two or three of the major advantages

and disadvantages of manual brakes for table saws : a . Advantages :

b. Disadvantages:

75
10b. What would you say are the major advantages and disadvantages

of an electronic brake on a table saw?

a . Advantages :

b. Disadvantages:

10c. What kinds of problems and advantages are you aware of when a manual brake is used on a radial arm saw?

a . Advantages :

b. Disadvantages

lOd. What about when an electronic brake is used on a radial arm saw?

a. Advantages:

b. Disadvantages

11. It appears that most table and radial arm saws have three-wire grounding

connections. Do you feel that it would be of any benefit to use double

insulated connections for these saws?

Yes No

11a. Why do you feel that way?

76
12. It is generally accepted that the intrcxiuction of ground fault interrupters to home electrical circuits provides an additional margin of safety

when electrical equipment is used. How would you rate the extent of this

added safety when using double insulated power tools?

Greatly increases safety

Moderate increase in safety

Marginal improvement in safety

No added safety

Benefits of GFI's unknown

12a. What about when using three -wire grounded power saws?

Greatly increases safety

Moderate increase in safety

Marginal inprovement in safety

No added safety

Benefits of GFI's unknown

13. Do you think that present saw designs provide adequate protection

against accidental triggering of the saw by children?

Yes No

13a. Which of the following do you feel should be considered as methods by which saws could be made "child resistant"?

Strong pressure requirement to activate switch

Multi-step ignition process; i.e., several operations

must be performed before saw starts

Locking system when saw is not in use for all saws Other (specify)

None of the above; no need for such precautions

77
13b. Would you prefer a locking device that is an integral part of

the ignition switch (i.e., something built into the switch) or one

that is external (i.e., such as a separate lock)?

Prefer lock that is part of the switch

Prefer lock that is external to the switch

Other (specify)

13c. How inportant would you rate ease and convenience of locking

and unlocking saws as related to using such a device?

Ver>' inportant

Slightly inportant

Doesn't matter

Other (specify)

14. When you consider the use of a rip fence by a beginner, would you say

that it is primarily: (Mark all that apply).

A safety feature

A convenience item

A "crutch" which he will learn to do without

Unnecessary

A necessity

Other (specify)

14a. How would you rate the rip fence on a table saw in terms of ease

of attachment and convenience of use?

Very easy to attach Very convenient to use Reasonably easy Reasonably convenient

Somevrfiat of a bother Somewhat of a bother

Other (specify) Other (specify)

78
14b. Would you say that aligning the rip fence on a table saw is:

Relatively easy

Somewhat difficult

Requires great concentration to properly align

Other (specify)

15. What optional features, such as guides and accessories, etc. would you

suggest for the novice operator of (a) table saws; and (b) radial arm saws?

a . Table saws :

b. Radial arm saws:

16. In your opinion, would there be any advantages to having a blade or arbor lock that would restrain the blade during changing?

Yes No

16a. Why do you say that?

17. Is it technically feasible to design an interlock system that would

prevent adjustments being made to a saw while the blade is rotating?

Yes Nk)

17a. What is your opinion on the desirability of such a system?

79
18. How much do you feel that dull blades contribute to accidents in

general and kickbacks specifically?

Accidents Kickbacks

Major cause Major cause

Moderate ainount Moderate amount

Limited extent Limited extent

Little or none Little or none

18a. A dull blade is made obvious to the experienced saw user by

poor quality cut, burning of material etc. Have you any ideas on ways to alert the casual user that his blade needs to be sharpened

or replaced?

Yes: Please explain:

No

19. Do you regard the sawdust ejection feature on radial arm saws as:

Functional

A convenience item

A safety feature

Unnecessary

A necessity

Other (specify)

19a. How about a vacuum system for removal of debris on table saws:

do you feel that this is:

Functional

A convenience item

A safety feature

Unnecessary

A necessity

Other (specify)

80
20. Table saws are often purchased without motors; the buyer supplies his

own. Ifow would you rate this practice in terms of over-all operational safety?

Very safe

Reasonably safe

Somewhat unsafe

Hazardous

Other (specify)

21. How would you rate the noise levels emitted during operation of a

table saw?

Excessively high

High

Acceptable

Low

Other (specify)

21a. How about the noise on radial arm saws?

Excessively high

High

Acceptable

Low

Other (specify)

21b. Are there any noise standards that you know of for stationary

saw operations?

Yes : What are they?

No

21c. Do you feel that a standard of this kind would be (is) helpful?

Yes No

81
22. Briefly, what factors do you think should determine the grip (feed

luindle) design and location on radial arm saws?

Grip design:

Grip location:

22a. Do you have any preference for one design and/or location? Why?

23. How would you rate the safety return feature available on some radial

arm saws?

Very safe

Reasonably safe

Slightly unsafe

Hazardous

Other (specify)

23a. Why do you say that?

24. The following questions deal with instruction or owner's manuals

provided with stationary saws. Please answer these items based on your

familiarity with the manuals and your personal opinions about their effectiveness.

24a. Would you say tliat the graphics that are used to demonstrate

various saw operations are:

Satisfactory

Need inprovement

Other (specify)

82
24b. Do you prefer sketches or photographs of the various details

presented in instruction manuals?

Sketches

Photographs

Other

24c. Would you say that the written instructions in the manuals are:

Satisfactory

Need improvement

Other (specify)

24d. For which of the following types of operations do you feel

graphic representation should appear in a manual

:

Rip cuts

Cross cuts

Pocket cuts

Identification of saw parts

Depth adjustment

Bevel adjustment

Use of rip fence

Use of miter gage

Resawing

Rabbiting

Dadoing

Cutting large pieces

Maintenance and care Other (specify)

24e. Could you suggest any ways to further alert the user to the proper

and safe operation of table and radial arm saws?

83
24f . How much do you feel that the lack of thorough reading of the

instruction manual contributes to accidents?

24g. What warnings do you feel should appear on the saw itself?

24h. The manuals of all members of the Power Tool Institute contain

a list of safety instructions developed by PTI. Are there any additional instructions or warnings you think should be included?

No

Yes, for exanple:

25. If you have any additional comments on questions or areas not covered

in the survey please use the following space. If needed attach additional

sheets.

THANK YOU FOR YOUR TIME AND EFFORT IN CCMPLETING THIS SURVl.T. YOUR OPINIONS

ARE MOST IMPORTANT TO US AND WILL BE TABULATED WITH THOSE OF THE OTHER

RESPONDENTS. NO INDIVIDUAL IDENTITIES OF EITHER RESPONDENTS OR MAMJFACTURERS

WILL APPEAR IN THE GENERAL SUNWARIES WE PLAN TO DEVELOP.

84
.AJ'PENDIX D2

Tabulation of Responses to Table and Radial Arm Survey

Survey items in this appendix are presented in abbreviated

form. See Appendix Dl for complete text.

85

Tabulation of Survey Responses: Table and Radial Arm Saws

1. Effectiveness of anti -kickback fingers on table saw:

- - Very effective.

3 - Moderately effective.

- - Relatively ineffective.

- - Provides no protection.

- - Introduces additional hazards.

la Effectiveness of anti -kickback fingers on radial arm saws:

- - Very effective.

2 - Moderately effective.

2 - Relatively ineffective.

- - Provides no protection.

- - Introduces additional hazard.

2. Functions of a splitter on:

a. Table saw:

3 - To keep kerf from closing and pinching blade.

b. Radial arm saw:

4 - To keep kerf from closing and pinching blade.

2a Effectiveness of splitter in preventing kickbacks:

Table Saws Radial Arm Saws

3. Other ways to protect saw user from kickbacks:

1 - Instructions, good manuals.

1 - Keep blade clean, sharp and in proper alignment.

4. Splitter problems when blades of varying widths used:

1 - Splitter imst be slightly thinner than kerf to function properly.

1 - Splitter thickness should be sized for thickest blade used.

4a iDther problems with splitter:

1 - Splitter must be properly aligned with blade.

- - pjctremely difficult for the novice.

- - Moderately difficult.

2 - Relatively easy.

2 - Very easy.

21 2

11

Very effective.

Moderately effective.

Relatively ineffective.

Does not prevent kickbacks.

5. Ease of aligning splitter:

87
6. Preferred material for splitter, why:

3 - Steel for durability and strength

7. Best type of table saw guard for various operations, safety as only

criterion:

Operation Best guard

Crosscutting short/medium length 2 - Splitter mounted, 1 - hinged

stock. overhead.

1 - One that covers all of blade not

engaged in cutting.

Crosscutting long stock. Same responses as above.

Ripping narrow boards. Same responses as above.

Ripping large plywood sheets. Same responses as above.

Non saw- thru operations. 1 - Barrier type, 1 - table mounted

1 - One that covers all of blade not

engaged in cutting.

Res awing. Same response as above.

7a What guards appropriate for special operations:

1 - Tunnel guards, custom fit to wood for repetitive operations.

1 - Dado and molding table inserts to support table and minimize blade

contact possibility.

7b With safety as only criterion, what is best single guard:

2 - Splitter mounted.

1 - Hinged overhead.

1 - One that would cover all of the blade not engaged in cutting the

material.

7c Is above guard impractical for home workshop use:

2 - No

2 - Yes - In what way:

1 - (Splitter mounted) - cannot be used for non saw- thru

operations.

1 T (Complete coverage) - would be difficult to adjust

for different applications.

7d If limited to one guard, the best in terms of safety, cost, ease of use,

versatility and reliability is:

3 - Splitter mounted,

1 - Hinged overhead type.

88
8. Effectiveness of retractable leaf guards on radial arm sau's:

- - Verv' effective.

2 - Moderately effective.

2 - Relatively ineffective.

- - Increases blade contact hazard.

8a Other types of guards for radial arm sau's:

1 - Tunnel guards for repetitive sau-ing.

1 - Fully enclosed, see-thru side guards.

1 - One that covers all of the blade not engaged in cutting material.

1 - Ant i -kickback device.

9. Does coastdov-Ti present hazard for table saw user:

1 - Yes - User may reach for work or scrap before blade stops.

2 - No - Coastdown duration only a few seconds, guard should protect,

9a Does coastdov,Ti present hazard for radial arm saw user:

2 - Yes - Operator may reach for v,ork or scrap, blade can move if

contact made with saw table.

2 - No - Coastdown time is very short, "danger zone" is readily

obvious

.

9b Any advantages to establishing a maximum braking time:

2 - Yes - 1-15 seconds.

1 - Time depends on blade size.

1 - No - Manual braking more appropriate.

10. Preferred braking systems:

'

For table saw For radial arm saw

1 Manual

1 Fleet ronic

1 (automatic) 1 (automatic) Other

2 1 None

10a Advantages § disadvantages of manual brakes for table saws:

a. Advantages:

3 - No advantages.

1 - Oieaper, possibly more reliable.

b. Disadvantages:

1 - Hand must be near moving blade to operate, brake parts may be

propelled like projectiles, mechanism must be complex to function

in any tilt or elevation position.

1 - Probably wouldn't be used regularly.

1 - Brake not necessary on table saw.

89
10b Advantages 5 disadvantages of electronic brakes for table saws:

a. Advantages: -

. 2 - No advantages.

2 - Takes braking function out of users hands.

b. Disadvantages:

2 - Expensive.

1 - Greater possibility of malfunction.

1 - Brake not necessary on table saws.

10c Advantages 5 disadvantages of manual brakes for radial arm saws:

a. Advantages:

1 - Relatively inexpensive.

1 - Keeps operator occupied till blade stops.

1 - Simple, uses no power when not is use.

1 - More reliable.

b. Disadvantages:

2 - May not be used.

2 - Hand reaches toward blade to operate.

lOd Advantages 6, disadvantages of electronic brakes for radial arm saws:

a. Advantages:

3 - Requires no operator initiated action.

1 - No advantages.

b. Disadvantages:

1 - Costly.

1 - Can spin off blade.

1 - Does not keep operator occupied until blade stops.

11. Any benefits from using double insulation for table and radial arm saws:

4 - No - If integrity of ground is assured grounding is best.

12. Extent of added safety provided by GFI's when using double insulated tools

- - Greatly increases safety.

- - Moderate increase in safety.

1 - Marginal improvanent in safety.

2 - No added safety.

1 - Benefits of GFI's unknown.

12a Extent of added safety provided by GFI's when using grounded saws:

- - Greatly increases safety.

2 - Moderate increase in safety.

1 - Marginal improven^nt in safety.

- - No added safety.

1 - Benefits of GFI's unknown.

90
13. Do present saw designs provide adequate protection against accidental

triggering of saw by children:

4 - Yes

0 - No

13a VVhat methods should be considered for making saws "child-resistant":

- - Strong pressure requirement to activate switch.

- - Nlilti-step ignition process.

3 - Locking system \^en saw is not in use for all saws.

- - Other

1 - None of the above, no need for such precautions.

13b Preference for ty^e of switch lock:

2 - Prefer lock that is part of the switch.

1 - Prefer lock that is external to the switch.

- - Other.

13c Importance of ease and convenience of locking and unlocking saws as related to using the device:

2 - Very important.

1 - Slightly important.

- - Doesn't matter.

- - Other.

14. Use of rip fence by novice saw user:

3 - A safety feature.

1 - A convenience item.

- - A "crutch" vvtiich he will learn to do without.

- - Unnecessary.

3 - A necessity.

- - Other.

14a Table saw rip fence ease of attachment and convenience of use:

2 - Very easy to attach. 2 - Very convenient to use.

1 - Reasonably easy. 1 - Reasonably convenient.

- - Somewhat of a bother. - - Somewhat of a bother.

- - Other. - - Other.

14b Alignment of table saw rip fence:

3 - Relatively easy.

- - Somewhat difficult,

- - Requires great concentration to properly align.

- - Other.

91
15. Recommended optional features and accessories for novice operator:

a. Table saws:

2 - Miter gauge, fence.

1 - Sanding disk, dado blades.

1 - Saw stand.

b. Radial arm saws:

2 - Special purpose blades and cutters.

1 - Saw stand.

16. Any advantage to blade or arbor lock for blade changing:

4 - No

0 - Yes

16a Why:

2 - Present 2 wrench system adequate.

1 - Could become accidentally engaged, resulting in wear or failure

of parts.

17. Is it technically feasible to design an interlock system that would

prevent adjustment

:

1 - Yes

2 - No

17a Desirability of interlock system:

3 - Not desirable.

1 - Would limit use of saw.

1 - Insignificant advantage for added expense and potential failure.

18. Contribution of dull blades to accidents:

In general Kickbacks

Major cause 1 1

Moderate ajnount 1 1 Limited extent

Little or more 2 2

18a Ideas about how to alert casual user that blade is dull:

1 - Save and display sample cut from new blade for comparison.

1 - Inspection of edge of teeth and set will advise.

19. Sawdust ejection feature on radial arm saws:

1 - Functional.

1 - A convenience item.

2 - A safety feature.

1 - Unnecessary.

1 - A necessity.

- - Other.

92
19a Vacuum system for removing debris on table saws:

- - Functional.

3 - A convenience item.

- - A safety feature.

1 - Unnecessary.

- - A necessity.

- - Other.

20. Operational safety of table saws purchased without motor, user supplies

power source:

- - Very safe.

2 - Reasonably safe.

- - Somewhat unsafe.

1 - Hazardous.

- - Other.

21. Noise level ratings - table saws:

- - Excessively high.

1 - High.

1 - Acceptable.

1 - Low.

- - Other.

21a Noise level ratings - radial arm saws:

- - Excessively high.

1 - High.

2 - Acceptable.

1 - Low.

- - Other.

21b Are you aware of any noise standards for stationary saw operation:

3 - Yes - 2 - OSHA

1 - ANSI 01.1 - 1971

1 - No

21c Would noise standards be helpful

:

2 - Yes

2 - No

22. Factors determining grip (feed handle) design and location on radial arm saws:

a. Grip design:

3 - Comfort.

1 - Functional.

1 - Conform to hand and arm of operator

93
b. Grip location:

1 - Away from immediate cutting area.

1 - In line with natural arm/body relation.

1 - Functional.

22a Preference for one design/ location:

2 - No

1 - All known units appear adequate.

23. Rating of "safety return":

- - Very safe.

- - Reasonably safe.

2 - Slightly unsafe.

2 - Hazardous.

1 - Other - unnecessary.

23a Reasons for ratings:

3 - Cutting head may move without operator control.

1 - Fatigue inducing.

1 - Increases effort required to pull saw through material when

crosscutting.

24. Adequacy of instruction manuals:

24a Adequacy of graphics:

3 - Satisfactory.

1 - Need improvement

.

- - Other

.

24b Preference in graphics:

1 - Sketches.

1 - Photographs.

2 - Other - both, line drawings.

24c Adequacy of wTitten instructions:

2 - Satisfactory.

2 - Need improvement.

24d Graphic representation should appear

4 - Rip cuts.

4 - Crosscuts.

4 - Pocket cuts.

4 - Identification of saw parts.

4 - Depth adjustment.

4 - Bevel adjustment.

3 - Use of rip fence.

3 - Use of miter gauge.

in manuals for:

4 - Resawing.

4 - Rabbiting.

4 - Dadoing.

4 - Cutting large pieces.

4 - Maintenance and care.

1 - Other - trouble shooting, safety

tips.

94
24e Ways to further alert user to proper and safe operation:

1 - Provide incentive to read instruction manuals.

1 - Include proper type of warning labels.

1 - Recommend attendance at shop courses.

24f Mow much does lack of thorough reading of manuals contribute to accidents:

1 - Very greatly.

1 - Greatly.

1 - Somewhat.

1 - Significantly for novice.

24g What warnings should appear on the saw itself:

1 - None.

1 - As required by UI. 987.

1 - Highly readable warnings at all potentially hazardous locations.

1 - Direction of rip, "make adjustments after saw stops," "make

sure all clamps are tight before cutting.

24h Recommendations for additional warnings in manual beyond those PTI members

now include:

3 - No.

1 - Yes - Include warnings specific to particular tool, PTI list

may be too general.

95

APPENDIX E

Power Saw Manufacturers Surveyed

Representatives of the following manufacturers participated in the

power saw surv^eys.

Portable Circular Saw Survey

AEG Power Tool Corporation

The Black and Decker Manufacturing Company

Ferrostaal-Ntetabo Tool Corporation

Millers Falls Company

Milwaukee Electric Tool Coi-poration

Robert Bosch Corporation

Rockwell International Corporation

The Singer Company

Sioux Tools, Inc.

Skil Corporation

The Stanley Works

Thor Power Tool Company

Table and Radial Arm Saw Survey

De Walt Division of the Black and Decker Manufacturing Company

Emerson Electric Company

Rockwell International Corporation

Toolkraft Corporation

USCOMM-MBS-DC 97

NBS-n4A (REV, 7-73)

U.S. DEPT. OF COMM. 1. IHIULK A 1 ION OR KKPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA ^ No. SHEET NBSIR 75-748

3. Recipient's Accession No.

4. TITLE AND SUBTITI.I-: Power Saws: A Review of Injury Data and Power Saw Industry

Survey

5. Publication Date July 1975

6. Performing Organisation ( ode

7. AUTHOR(S)

V. J. Pezoldt, J. J. Persensky

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4411423

11. Contract /Grant No.

12. Sponsoring Organization Name and ( ompleie Address (Street, City, State, ZIP)

Consumer Product Safety Coninission

Washington, D.C. 20207

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Lode

15. SUPPLEMENTARY NOTES

16. ABSTRA(;T (A 200-word or less (actual summary of moat ai^ftificmnt inlomation. If document includes a significant

bibliography or literature survey, mention it here.)

Two activities of an investigation of power saws are described: a review of

power saw injury data and two surveys of saw manufacturers' opinions concerning safety

aspects of saw use and design. The injury data reviewed consisted of information from

Liie iNdLxuiiai. cxcvuiunxc injury ourvcixxonce oystcni ana rrran suniuaries or mueptn

Investigation Reports compiled by the Consumer Product Safety Conmission. The two

surveys, dealing with portable cirailar saws and table and radial arm saws respectively,

were directed toward obtaining the opinions of technical representatives of power saw

manufacturers on five major areas of saw use and design, i.e., electrical safety, blade

contact hazards and prevention, accidental starting, the design of various saw

components and the judged adequacy of saw instruction manuals. Power saw engineers

and designers recognize some problems with present saw designs, especially relating to

kickbacks. Overall, however, the survey respomients believe saws to be reasonably

free from hazards introduced by product design. The area in v^iich the saw manufacturers

believe the most hazards to exist is that of the operator's use of power saws. This

human element in saw accidents is recognized as a major contributor to saw related

injuries, but little is known about how to assure that safe practices will be

followed. Areas for further study are suggested.

17. KEY WORDS (six to twelve entries; alphatxtical order; capitalize only (he first letter of the first key word unless a proper name; separated by semicolons

)

Accident research; consumer products; injury data;

opinion survey; portable circular saws; power saws; radial am saws; safety;

table saws.

18. AVAILABILITY Unlimited

1

' For Official Distribution. Do Not Release to NTIS

(

' Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C, 20402. SD Cat. No, CI 3 ^ ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

102

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$5.25

USCOMM-DC 2e042-P74